Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$52.76	9.338%	$57.6867	$57.69	$57.70	$57.70
Purchase #2	$22.75	5.676%	$24.0413	$24.04	$24.05	$24.00
Purchase #3	$141.81	11.350%	$157.9054	$157.91	$157.90	$157.90
Purchase #4	$40.44	5.115%	$42.5085	$42.51	$42.50	$42.50
Purchase #5	$162.47	7.617%	$174.8453	$174.85	$174.85	$174.80
Purchase #6	$71.37	10.612%	$78.9438	$78.94	$78.95	$78.90
Purchase #7	$158.70	9.110%	$173.1576	$173.16	$173.15	$173.20
7 purchase totals =	$650.30		$709.0886	$709.10	$709.10	$709.00